Continuously rotatable microwave phase shifter



Feb. 26,1957

R. M. WHITEHORN CONTINUOUSLY ROTATABLE MICROWAVE PHASE SHIFTER Filed Jan. 3, 1952 RICHARD M. WHITE RN INVENTO ATTORNEYS CONT INU OUSLY ROTATABLE MICROWAVE PHASE SHIFTER Richard M. Whitehorn, Baltimore, Md., assignor to Bendix Aviation Corporation, Towson, Md., a corporation of Delaware Application January 3, 1952, Serial No. 264,7 09

Claims. (Cl. 333-31) This invention relates to devices for the continuous rotation of the phase of microwave energy.

It is an object of the invention to provide means for the continuous rotation of the phase of microwave energy which will be simple, accurate and rugged.

It is a further object of the invention to provide such a means which will provide continuous phase shift as a precise linear function of a shaft rotation.

These and other objects and advantages of the invention are realized by a system in which a plane polarized wave is injected into a section of circular wave guide in a manner to excite in the latter a circularly polarized wave form. The circular wave guide is terminated in a rotatable shorting plunger carrying on its face a quarterwave plate. The wave reflected from this plunger will be rotatively polarized in the opposite sense to that of the incident Wave; The reflected wave is removed from the wave guide at a point at which there will be a minimum of interaction between the applied and reflected waves.

In the drawing:

Fig. l is a perspective view of a phase shifter embodying the invention and in which energy is applied and removed from the phase shifter by a pair of collinear rectangular branch Wave guides;

Fig. la is an elevational view of a fragment of the device of Fig. 1 showing the relationship of some of its parts;

Fig. 2 is a perspective view of a modification of the phase shifter of Fig. 1 in which energy is applied and removed by a pair of rectangular wave guides, one joining the phase shifter along its axis and the other joining it at right angles thereto; and

Fig. 3 is a perspective view of another modification in which T junctions are employed for joining the energy applying and removing elements to the phase shifter.

In the embodiment of Fig. 1 the phase shifter comprises a circular wave guide section 1 which is closed at one end by a short circuiting plate 2 and at the other end by a short circuiting plunger 3. The plunger 3 is mounted for rotation in a bearing 4 and is provided with the usual quarter-wave choke groove 5 to prevent losses due to leakage around its circumference.

Extending from the plunger 3 is a shaft 6 by which it is rotated. Mounted on the inner face of the plunger is a quarter-wave plate 7. The plate 7 is coaxial with the wave guide 1. The end effects caused by the quarterwave plate are unimportant so long as it is kept thin.

Joining the wave guide 1 at a point which is an eifective quarter-wave length from the shorting plate 2 is a pair of collinear, rectangular wave guides 8 and 9. These wave guides have a common plane of symmetry normal to the lines of electrical intensity therein when-they are excited in the TEM mode. This plane makes an angle 0 with the axis of the wave guide 1, such that excitation of the branch 8 in the T1301 mode will excite, in the wave guide 1, a circularly polarized wave which will travel 2,783,439 Patented Feb. 26, 1957 towards the shorting plunger 3 with a right-handed rotation and toward the shorting plate 2 with a left-handed rotation. Fig. 1a illustrates the angular relationship of wave guides 1 and 8.

In the operation of the device of Fig. 1 the wave guide 8 is excited in the TEM mode which results in the exciting of the circular wave guide 1, in the manner described above. The left-handedly polarized energy is reflected by the shorting plate 2 and the reflected wave will be of a right-handed polarization and will reenforce the wave travelling toward the shorting plunger 3. The wave guide 9 will not be excited by this energy, since it will only accept energy polarized in a left-handed sense travelling from the direction of the shorting plunger 3.

Energy reaching the plunger 3 will be reflected with left-handed polarization and, hence, will be accepted by the wave guide 3, setting up the T1501 mode therein. Rotation of the shaft 6 will cause the phase of the wave excited in the Wave guide 9 to continuously change, the relative phase of the waves in the wave guides 8 and 9 being a linear function of the position of the plate 7. There will be no loading effect on the wave guide 8, since this guide will only be affected by energy from the direction of the plunger which is right-handedly polarized.

The large radius bearing 4 provides a precise and rugged system for rotation of the plunger 3 and its plate 7.

The method of determining the value of the angle 0 will be found described on page 374 of the text book Microwave Transmission Circuits by Ragan, which is vol. 9 of the Radiation Laboratory Series published in 1949 by McGraw-Hill Book Company, New York city.

Figs. 2 and 3 show other means for exciting right and left-hand circularly polarized waves of the TE11 mode in the circular wave guide. In Fig. 2 a rectangular wave guide 10 joins the circular wave guide 1 at the end remote from the shorting plunger, the two guides being coaxial. The wave guide 10 is shown with its H-plane horizontal. The TEM mode in this wave guide will excite in the circular wave guide a plane polarized wave with a vertical electric vector which can be resolved into components inclined by 45 to each side thereof.

Joining the circular wave guide an integral number of effective quarter-wavelengths from the end is a second rectangular wave guide 11. The H-plane of this guide contains the axis of the circular wave guide and is normal to the H-plane of wave guide 10. With this spacing and orientation the two rectangular wave guides will not load each other.

Between the wave guide 11 and the shorting plunger there is located in the wave guide 1 some means of establishing circular polarization in the wave set-up from the wave guide 16. This may be a quarter-wave plate or slab of dielectric material as shown at 12 which extends parallel to the axis of the wave guide and is inclined at an angle of 45 to the electric vector. A description of a quarter wave plate and the manner of its design may be found on page 371 of the above mentioned text book Microwave Transmission, Circuits. The slab or plate is so dimensioned, in accordance with principles known to the art, as to shift the phase of one component of the wave by This sets-up a circular polarization of, say, a right-handed sense.

The circularly polarized wave is reflected by the rotating shorting plunger 3, as in Fig. 1, the reflected wave being circularly polarized in the opposite sense and having a phase which is a linear function of the instantaneous position of the plate 7. As the reflected wave passes the plate 12 it is converted back to plane polarization and the plane polarized wave is removed by the wave guide 11. The wave in passing the plate 12 will undergo a second 90 phase shift in the component which was shifted by 90 during the initial passage. The resultant electric vector will now be'horizontal rather than vertical and the wave will excite in the wave guide 11 a wave of the TEm mode having a phase which continuously changes with the rotation of the plunger 3. The relative phase of the waves in the wave guides and 11 will be a linear function of the position of the plate 7.

Fig. 3 shows a modification similar to that of Fig. 2 except that the means for coupling plane polarized energy to the circular wave guide and removing it therefrom are symmetrical. A loop 13 of rectangular wave guide having its ends joining the top and bottom of the circular wave guide is provided for coupling a plane polarized wave into the latter. .At the junction points the H-plane of the rectangular wave guide contains :the axis of the circular .guide. The junction points lie 21 quarter-wavelength from the end of the circular wave guide. For the abstraction of plane polarized energy a similar wave guide loop 14 is joined to the guide 1 a half-wavelength from the guide 13 towards the plunger 3, the junction being made at each side of the guide 1.

The operation of this form of the invention is the same as that of Fig. 2. The arrangement for coupling energy to and from the circular wave guide is the most satisfactory of the three as far as losses go. It is, however, the most complex, and thus the costliest of the grOUP- They all provide mechanical ruggedness, which is .a factor of considerable importance in devices of this category.

What is claimed is:

1. A continuously rotatable microwave phase shifter comprising a circular wave guide, a rotatable short circuiting plunger in said waveguide, said plunger being journalled in one end thereof, a quarter-wave plate mounted on the face of said plunger in symmetry with respect thereto and for rotationtherewith, said plate having its axis of differential phase shift parallel to the axis of said plunger, wave guide means coupling a plane polarized wave to said circular wave guide in a manner to excite therein a circularly polarized wave travelling towards said plunger and wave guide means coupled to said circular wave guide in a manner to have excited therein a plane polarized wave'by the incidence therein of the wave reflected from said plunger. 7

2. A continuously rotatable microwave phase shifter comprising a circular wave guide, a rotatable short circuiting plunger in said waveguide, said plunger being journalled in one end thereof, a quarter-wave plate mounted on the face of said plunger in symmetry with respect thereto and for rotation therewith, said plate having its axis of differential phase shift parallel to the axis of said plunger, means applying plane polarized energy to said circular wave guide and exciting therein in response to such application a circularly polarized wave travelling towards said plunger, and means converting energy reflected from said plunger to a plane polarized wave and removing said converted energy from said wave guide.

3. A continuously rotatable microwave phase shifter comprising a circular wave guide, a rotatable short circuiting plunger in said waveguide, said plunger being journalled in one end thereof, a quarter-wave plate mounted on the face of said plunger in symmetry with respect thereto and for rotation therewith, said plate 4 having its axis of differential phase-shift parallel to the axis of said plunger, means including a first rectangular 'wave guide applying plane polarized energy to said circular wave guide and exciting therein in response to such application a circularly polarized Wave travelling towards said plunger, and means including a second rectangular wave guide converting energy reflected from said plunger to a plane polarized Wave and removing said converted energy from said circular Wave guide, said rectangular wave guides being joined to said circular wave guide with such relative orientation and spacing that each is substantially non-responsive to energy existing in the other.

4. A continuously rotatable microwave phase shifter comprising a circular waveguide, a rotatable short circuiting plunger terminating one end of said waveguide, a quarter wave plate mounted on the face of said plunger for rotation therewith, said plate being located in symmetry with respect to said plunger and having its axis of differential phase shift parallel to the axis of the plunger, a shorting plate terminating the remaining end of said waveguide, means coupling a plane polarized wave to said circular waveguide in a manner to excite therein a circularly polarized wave travelling towards said plunger, and rectangular waveguide means coupled to said circular waveguide in a manner to render said waveguide means selectively responsive to the incidence of wave energy travelling away from said plunger and circularly polarized in a sense opposite to that of .said wave travelling toward said plunger.

5. Means for shifting the phase of plane polarized energy in a rectangular waveguide as a function of the rotation of a shaft comprising, a circular Waveguide interrupting said rectangular waveguide, a plunger mounted on and coaxial with said shaft, the face of said plunger terminating one end of said circular Waveguide, a quarter wave plate mounted on said face of said plunger for rotation therewith, said plate being located in symmetry with respect to said plunger and having its axis of differential phase shift parallel to the axis of the plunger, and a short circuiting plate terminating the remaining end of said circular waveguide, the axis of said circular waveguide lying in a plane normal to the axis of said rectangular waveguide, the plane of symmetry of said rectangular waveguide normal to the lines of electrical intensity of the energy therein making an angle with the axis of said circular waveguide such that the incidence of the said plane polarized energy of said rectangular waveguide will excite in said circular waveguide a circularly polarized Wave travelling toward said plunger.

References Cited in the tile of this patent UNITED STATES PATENTS 2,438,119 Fox Mar. 23, 1948 2,526,383 Meier Oct. 17, 1950 2,564,030 Purcell Apr. 14, 1951 2,593,120 Dicke Apr. 15, 1952 2,606,248 Dicke Aug. 5, 1952 2,686,901 Dicke Aug. 17, 1954 OTHER REFERENCES Ragan: Microwave Transmission Circuits, vol. 9, M. I. T. Rad. Lab. Series, published 1948, McGraw- Hill Co., pp. 369-79. 

